1. FIELD OF THE INVENTION
This invention relates generally to apparatus for conveying particulate material (such as gunite, refractories etc.) to and through a delivery tube--and more particularly relates to such an apparatus usable with modernly favored constituents (e.g. silica fume) that are especially susceptible to clogging and to dust emission.
2. RELATED ART
Seminal work in this field is memorialized in 1964 U.S. Pat. No. 3,161,442 of Frank A. Reed. He devised a rotary feed structure in the form of a segmented rotating bowl, to carry particulate material from a hopper to a delivery tube--with compressed-air expulsion of the material from U-shaped passageways or "pockets" of the feed bowl into the delivery tube.
Strengths of Reed's system are that only one relatively small area about the expulsion station must be sealed to constrain the compressed air and the material, and gravity tends to retain the material in the bowl (thus minimizing deterioration of the seal) until the material reaches the expulsion station.
Analogous European developments aimed for different benefits, settling on a straight-through rotary structure that tends to be clog resistant (though not entirely immune) because it is gravity-assist-emptied as well as gravity-filled, and because the particulate material need not negotiate hairpin curves within the feed chambers.
The European configurations, however, are inherently bulkier vertically and employ two very large seals, at top and bottom respectively. The highly abrasive material to be dispensed is gravity-loaded against the lower seal, which is therefore subject to extreme wear.
Reed's patent is hereby fully incorporated by reference into this document, as is 1991 U.S. Pat. No. 5,150,991--coowned with the present document by Reed Manufacturing, Inc.--which introduced very important refinements directed to control of the compressed-air-and-material sealing system.